1. Field of the Invention
The invention relates to a surface light source device, and more particularly to a backlight for a liquid crystal display (LCD) that provides improved assembly efficiency and better overall light characteristics.
2. Description of the Related Art
As a display device, a liquid crystal display (LCD) is not luminous itself and generally requires a backlight device for illumination. Accordingly, performance of the LCD is greatly dependent on the backlight device employed.
U.S. Pat. No. 6,513,944 issued to Chou discloses a conventional backlight device. FIG 1A of the Chou patent shows that this conventional back light device comprises a first frame 1, a diffuser 2, a light guide 3, a reflection sheet 4, a second frame 5, a back plate 6 and two lamp assemblies 7. FIG. 1B of the Chou patent shows each lamp assembly 7, including two fluorescent tubes 72, a tube guard 71 covering the fluorescent tubes 72, and a holder 73 for fixing the fluorescent tubes 72 in the tube guard 71.
FIG. 4A of the Chou patent shows an assembly of the light guide 3, the reflection sheet 4 (not visible), the second frame 5 and the back plate 6. The diffuser 2 and the first frame 1 are not included. The lamp assemblies 7 are inserted from an open end 57 of a groove 51 of the second frame 5 to a closed end 56 thereof. A screw 62 (shown in FIG. 5 of the Chou patent) is screwed into a hole 64 provided through the back plate 6 to fasten each lamp assembly 7 in the groove 51.
It is important that a distance between the fluorescent tubes 72 of the lamp assemblies 7 and the light guide 3 be accurately maintained at a designed distance, otherwise: (a) the light emitted from the upper portion and lower portion of the light guide 3 will be too strong due to the fluorescent tubes 72 being too close to the light guide 3, or (b) the light emitted from the upper portion and lower portion of the light guide 3 will be too weak due to the fluorescent tubes 72 being too far away from the light guide 3. In summary, if a relative position of the light guide 3 and the fluorescent tubes 72 is not accurately kept as designed, the overall performance of the backlight device will be poor.
Also referring to FIG. 5 of the Chou patent, to reliably retain the relative position of the fluorescent tubes 72 and the light guide 3, the prior art back light device needs the second frame 5, the back plate 6, the tube guard 71, the holder 73 and the screw 62 which screws into the hole 64 cooperating together to fix and establish the relative positions of the fluorescent tubes 72 and the light guide 3. The assembly/disassembly of the back light device is complicated and requires an excessive amount of time since it has so many components. Furthermore, it is difficult to accurately control the relative positions of the light guide 3 and the fluorescent tubes 72 according to their design specifications.